Questions tagged [computational-physics]

Computational physics is the study and implementation of numerical algorithms to solve problems in physics for which a quantitative theory already exists.

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1answer
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Calculation of Mean Square Displacement for Brownian dynamics system with Lennard Jones interactions in python3

I have a problem getting a sensible result for the Mean Square Displacement (MSD) for a simulation of $N$ particles under Brownian dynamics with Lennard-Jones interaction between them with or without ...
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0answers
14 views

Propagation of a Gaussian beam using FFT

I am trying to simulate the propagation of a gaussian beam through a lens using an FFT approach. I tried to implement the approach described by Couairon in this paper at page 43: https://link....
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2answers
152 views

How to simulate over 1 billion particles?

I want to simulate human erythrocytes in capillaries. I calculated, that for a 1 meter long and 1 mm in diameter capillary there are about 3 billion blood cells. Erythrocytes are actually discs, but ...
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0answers
56 views

Simulating an object in orbit

This question is more oriented around suggestions for simulation tools and how to approach simulating an object in orbit. So high level I am trying to simulate the concept of a Sky Hook. What are the ...
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0answers
49 views

Is it possble to do this complex symbolic calculation with Matlab?

Sorry it's bit abrupt, but recently I am caught up in some symbolic calcualtion which is tedious and almost impossible with mere human hands, so just wondering is it possible to solve the double ...
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1answer
67 views

Defining Current Density in a FEM model (MATLAB)

I'm attempting to solve the Poisson equation in 3D for a magnetic vector potential in the presence of a current source. To validate my code, I'm initially looking to reproduce the model described in ...
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0answers
23 views

non premixed Combustion by using oxygen droplets

I am trying to simulate a case in ANSYS FLUENT for combustion of methane and oxygen where oxygen enters the domain in the form of droplets. There is a change in temperature but there is no formation ...
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0answers
52 views

Radial Hartree and exchange-correlation potentials

According to [1] the one-dimensional Kohn-Sham equation is given by $$ \left( -\frac{1}{2} \frac{d^2}{dr^2} + \frac{l(l+1)}{2r^2} + V[\rho;r]\right) rR_{nl}(r) = \varepsilon_{nl} rR_{nl}(r) $$ where $$...
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42 views

Troullier-Martins pseudopotential with nonzero angular momentum quantum number

According to [1] the Troullier-Martins pseudopotential for quantum number $l$ is computed by $$ V^{\textrm{KB}}_{\textrm{nonlocal},l}(r) = \frac{\vert{}V_{\textrm{nonlocal},l}(r)\Phi^{\textrm{PP},0}_l(...
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1answer
579 views

Help with Fourier beam propagation method

I am working on implementing the Fourier beam propagation method in C++. I am really more of a programmer than a physicist but I think I have a good understanding of what I am trying to do. Here is ...
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1answer
954 views

Conserving Energy in Physics Simulation with imperfect Numerical Solver

I am creating a C++ Physics Simulation where I need to move an rigid body through an acting force field. Problem: simulation does not conserve energy. Quesiton: abstractly, how is conservation of ...
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60 views

Computation of Troullier-Martins pseudowavefunctions

The computation of Troullier-Martins pseudowavefunctions has been described in [1]. The pseudowavefunction $R^{\textrm{PP}}_l$ is defined by $$ R^{\textrm{PP}}_l(r) = \left\{ \begin{array}{ll} R^{\...
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1answer
52 views

Numerical Solution to Rayleigh Plesset Equation in Python

I have been trying to numerically solve the Rayleigh-Plesset equation for a sonoluminescence bubble in Python. You can read about this phenomenon here: https://iopscience.iop.org/article/10.1088/0143-...
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138 views

Ising model simulation offset critical temperature and interal ernergy

I'm writing a code for the Ising model using WHAM (the weighted histogram analysis method),But it seems to produce critical temperature and internal energy wrong. (newest rewritten code is below) <...
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1answer
84 views

Numerical bottlenecks

On a desktop scale computer, what are the most important bottlenecks (RAM vs. CPU, single vs. multithread) for numerical calculations? I'm specifically most interested in exact diagonalization and ...
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0answers
35 views

How to avoid density getting “deleted” in two way rigid body coupling with LBM CFD?

I've been reading this paper recently, which talks about using Lattice Boltzmann methods and two way coupling. Specifically, it outlines fluid solid coupling, and solid fluid coupling, and how simply ...
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0answers
120 views

Is a complete bacteria simulation with an exascale supercomputer possible?

Will it be possible to simulate a complete (at least simple) bacteria atom by atom on an exascale supercomputer? or is it possible already today with the largest systems? Here, I've read that ...
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0answers
52 views

Using MATLAB to simulate the Ising Model

I am using MATLAB to simulate a 1D Ising Chain. I am running into an issue where when trying to find heat capacity, my system has a tremendous amount of noise. I'll post my code and an image of the ...
3
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1answer
143 views

Consumer hardware for scientific computing?

I'm interested in problems around probability, statistics, and statistical mechanics, and often I find it useful to perform simulations to get some sense of the underlying phenomena. Example ...
2
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1answer
43 views

Numerical integration of the dataset of a function

The energy equation for a spherically symmetric system is given by $$\mathscr{E}=\frac{v^2(r)}{2}+\frac{c_s^2(r)}{\gamma-1}+\phi(r)$$ where $\mathscr{E}$ is the total energy, $v$ is the velocity of ...
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1answer
74 views

Evaluating an indefinite integral that has no closed form

I need to evaluate the following indefinite integral: $$I=\int\frac{x^5+2ax^3+a^2x-4a}{x^7+ax^5+2ax^4}dx=\int\frac{x^5+2ax^3+a^2x-4a}{x^4(x^3+ax+2a)}dx$$ The solution that I obtained while ...
3
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1answer
336 views

General case Kutta condition

I'm working on a 2D inviscid fluid simulation using a "panel method", with Potential being used to enforce the no-through boundary condition. I'm trying to incorporate the Kutta condition, which says ...
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1answer
304 views

1-D turbulent energy spectra in homogeneous direction (non-isotropic)

I am trying to compute the one-dimensional energy spectra for my channel-flow simulation. I have already written a post-processing script to achieve this; however, I need to validate my code before ...
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1answer
45 views

Smoothed Particle Hydrodynamics: Weird clustering of particles. Is that normal?

I implemented a rather simple SPH simulation using a cubic-spline-kernel and a simple non-iterative pressure solver as described in this PDF in equation 9. I followed algorithm 1 of that paper (...
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1answer
66 views

Manual for library Libxc

Where can I find the manual for software library Libxc for exchange-correlation functionals? Links with domain www.tddft.org don't work.
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0answers
29 views

solving electron motion in undulator by Boris method

I am trying to use Boris scheme to solve the electron trajectory in undulator. The undulator field I used is: $$B_x = b_0\sin(2\pi \tfrac{z}{\lambda_u})$$ where $b_0 = \dfrac{2\pi c_{0}K}{q m_{e} \...
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1answer
118 views

Runge-Kutta fourth order method. Integrating backwards

I am using a Runge-Kutta fourth order method to solve numerically the usual equation of motion of a background scalar field in curved spacetime with a quartic potential: $\phi^{''}=-3\left(1+\frac{H^{...
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1answer
96 views

For a determined (known) Space charge density, what are the conditions to obtain the Electric potential/field distribution? (COMSOL, MATLAB)

Theoretic part From the theory, in Electrostatics inside a real dielectric material between real conductors, in a simple 1D plane geometry between points $P1$ and $P2$, according to the current ...
3
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1answer
589 views

Numerical Sensitivity in Density of States of Tight-binding model

I'm working with the tight-binding model, and I'm trying to learn the basics of how to compute the Density of States (DOS) $N(E)$ numerically. The DOS is given by $$N(E) = \frac{1}{N}\sum_k \delta(...
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1answer
52 views

Should the derivative of an array be calculated array by array or element by element in CFD codes?

I am making my own finite difference computational magnetohydrodynamic code in Fortran 90. Looking at other codes they appear to calculate for example their $x$-derivatives, bb of their variables, e.g....
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1answer
352 views

Difficult bug in my 2D Compressible Euler solver

For the past few days, I have been writing a numerical solver for the 2D compressible Euler equations for an ideal gas. My numerical method has been the Local Lax Friedrichs or "Rusanov's method." ...
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1answer
63 views

ISING2D with Mathematica. Searching a correct way to compute the heat capacity (mean values over several iterations)

I'm trying compute the heat capacity $C_v$ out of my simulation for the 2D-Ising model which is given by $C_v = \frac{\langle E^2 \rangle - \langle E \rangle^2}{T^2N^2}$ ($E$: Energy, $T$: ...
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0answers
101 views

Heisenberg Model python : Specific heat capacity for spin 2

I have the correct plot for specific heat capacity when I am using the formula which is $C_V$ = differentiation of entropy with respect to temperature. However, When I try to calculate $C_V$, by using ...
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0answers
34 views

Pseudospectral method for Rayleigh-Benard with constant temperature gradient

$$ \nabla\cdot \mathbf{u} = 0 \\ \frac{\partial \mathbf{u}}{\partial t}+\left(\mathbf{u}\cdot \nabla\right)\mathbf{u} = -\nabla p+\nu\nabla^2\mathbf{u}+\alpha g\theta\mathbf{e}_z\\ \frac{\partial\...
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0answers
37 views

What is the best methodology for physics simulators of large floating base rigid body systems?

I want to implement a physics simulator for large floating base rigid body systems from scratch. The Rigid Body Dynamics Systems (RBD) should typically have the following characteristics: About ~50 ...
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1answer
143 views

Problem concerning a part of a simulation for the Ising Model

I was wondering if anyone could help me with a simulation in Python (there is a small part of the code where I have a question) about the Ising model. First, I wanted to get the magnetization $M$ ...
29
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16answers
9k views

Good examples of “two is easy, three is hard” in computational sciences

I recently encountered a formulation of the meta-phenomenon: "two is easy, three is hard" (phrased this way by Federico Poloni), which can be described, as follows: When a certain problem is ...
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0answers
48 views

Simulate friction arround steady-state point

When simulating a friction dynamic system, I have come to a problem when approaching steady-state. In the example below, a box moves along a surface with a certain friction coefficient: ...
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1answer
78 views

Computer build for scientific or big data computing [closed]

I'm wanting to build a computer for scientific or big data computing (Python, Fortran, Matlab) and I was hoping to get some advice on the type of processor, memory, graphics, etc I would need. I ...
2
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1answer
83 views

Langevin equation in 4th order Runge-Kutta

I'm trying to figure out how to translate a piece of code from Velocity Verlet to Runge-Kutta, while treating the time step dependence of the thermal noise correctly. The Langevin equation for my ...
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1answer
31 views

How to implement the Impulse Based Dynamics for the rigid body dynamics simulation?

I am having hard time learning the method of impulse based dynamics developed by Mirtich for rigid body dynamics simulation. Please help me out if any body has any example code(algorithm) of it. ...
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0answers
30 views

A preconditioner for self-consistent iteration

I tried to derive a preconditioner for self-consistent iteration similar to section IX in arXiv:0804.2583. For simplicity, consider here only one orbital (one or two electrons) systems. Suppose that ...
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0answers
65 views

Computing a double Integral using two Riemann sums & graphing multiple isosurfaces

I'm trying to compute the potential and electric field of a uniformly charged spherical shell and plot the results in the space outside the shell using MATLAB. I've tried everything from for loops to ...
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0answers
77 views

Solved : Damped spring-mass system, wrong position, correct speed and acceleration

I am modulating a spring-mass system with gravitation and aero drag, with python programming. The spring is hanging vertically and attached a weight. The user then selects a length to drag it down ...
3
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1answer
105 views

Doubt about Python code for calculation of Energy Conditions in General Relativity

In General Relativity, one possible way to decide if a space-time [i.e. a Lorentzian Manifold $(\mathcal{M}, \textbf{g})$ where $\textbf{g}$ is an arbitrary metric tensor.] is a "resonable physical" $[...
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1answer
463 views

ground state from the Schroedinger equation with a central potential what happens to the origin

I have code that attempts to implement a solution to the Schrödinger equation where there is a central potential (more or less im thinking of hydrogen), in 1-D using the numerov method to construct ...
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0answers
27 views

How can I implement the Invaded Cluster Algorithm for a network of Ising spins?

My primary concern is about finding the percolating cluster for any given network. For a lattice it is straight forward : When the size of a cluster reaches the length of the lattice, then it is said ...
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0answers
13 views

Compute cell values and isosurface constant from density values of particles

I am trying to reconstruct the surface for a fluid simulation based on a list of particles using the Marching Cubes algorithm. From different resources, such as http://paulbourke.net/geometry/...
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1answer
49 views

How to do Weierstrass-transform in MATLAB?

I have a diagonalization problem. I have the eigenstates correctly, and I want to do a Gaussian-smearing (Weierstrass-transform) on them. So I have the wave functions ($\Psi$), and the continuous ...
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1answer
57 views

Simulating magnetic particles in a field free point generated by two opposing magnets

This is probably a long shot with such a short time, but I've been trying to get theoretical data for a project I'm working on. The project involves using a very simplified version of magnetic ...